I don't think it's intended to be placed down like other blocks. So far I've only seen it hacked into the game, rather than occurring naturally. Maybe it works more like the portal blocks, where it only occurs inside of a frame?

Hold everything! Remember the image that was posted with this caption ("Well, that effect ended up being a LOT of work for something you will almost never see...")? It came with this texture as well. And if this block is a single plane of texture with seemingly infinite depth, could this be a texture for the void (when you dig below bedrock, this appears)?